Combustion of fossil fuel causes NOx emissions. NOx negatively impact the environment, for example by generating smog and acid rain. NOx emissions must thus be counteracted.
A number of technologies exist to counteract NOx emissions, these include:
combustion control systems for low NOx emissions;
selective catalytic reduction technology (SCR). This technology provides for supply of a reagent in the combustion gas and its reaction with NOx at a temperature between 300 and 400° C. and in the presence of a catalyst to convert NOx into N2 and water;
selective non-catalytic reduction technology (SNCR).
This technology provides for a reagent supply into the combustion gas and its reaction with NOx at a temperature between 800-1000° C. to convert the NOx into N2 and water. In this case, no catalyst is provided.
U.S. Pat. No. 5,681,536 discloses a lance for injecting air and a reagent for SNCR into a boiler.
US 2005/0 051 067 discloses a boiler with burners and nozzles for overfire air injection (i.e. injection of a part of the combustion air in the furnace above the burner belt to enhance primary NOx reduction). A reagent for SNCR is supplied together with the overfire air into the furnace.
WO 02/04349 discloses to inject overfire air and a SNCR reagent into a boiler, and contacting the combustion gas with the overfire air and SNCR reagent to decrease the concentration of nitrogen oxides therein. The reagent is provided in an aqueous solution or powder which is injected into the furnace with the overfire air.
The known technologies imply a large reagent consumption and thus large costs associated to the reagent.